In
TurboTax, when going through Personal Info section, you can select Foreign or U.S. Possession as his state of residence - since no state is listed, he doesn't have to file any state tax return.
Note: If you have dependents, or qualify for the Earned income Credit... Please count your overseas months as months inside the U.S. U.S.
military personnel stationed outside the United States on extended active duty
are considered to live in the United States during that duty period.